Influence of helium incorporation on growth process and properties of aluminum thin films deposited by DC magnetron sputtering

The effect of helium content on the morphology, crystallinity, and composition of aluminum films was investigated by depositing He-loaded Al films onto Si substrates via direct current (DC) magnetron sputtering in different Ar/He plasma mixtures. Three different plasma regimes were identified depending on the percentage of He in the gas phase. For a low He to total gas ratio (Gamma(He) <= 70%), the plasma is dominated by argon, where Ar+ ions contribute to sputter out the target atoms. The films deposited in this regime exhibited the classical dense columnar structure and contain very low amount of He (below 2%). Then, as Gamma(He) increases, helium ions begin to be formed and more fast He neutrals reach the substrate, affecting the film growth. As He amount increased in the gas phase up to 95%, the proportion of He inserted in the films rised up to similar to 15 at. %. Moreover, bubbles/porosity were formed inside the films; those obtained in pure He plasma presented a highly porous fiberform nanostructure. All results confirmed that the modification of the film characteristics was related to the change of the deposition conditions when Ar was replaced by He and to the insertion/release mechanisms of He during the growth.

Automated summary

The morphology, crystallinity, and composition of aluminum films can be influenced by the helium content, where an increase in helium leads to the formation of bubbles and porosity. This modification is attributed to the replacement of argon with helium and the insertion/release mechanisms of helium during film growth.